Only a limited number of molecules with demonstrated therapeutic value can be transported through the skin via unassisted or passive transdermal drug delivery. The main barrier to transport of molecules through the skin is the stratum corneum (the outermost layer of the skin).
Devices including arrays of relatively small structures, sometimes referred to as microneedles or micro-pins, have been disclosed for use in connection with the delivery of therapeutic agents and other substances through the skin and other surfaces. The devices are typically pressed against the skin in an effort to pierce the stratum corneum such that the therapeutic agents and other substances can pass through that layer and into the tissues below.
Issues related to applying microneedles include the ability to effectively insert the needles to a desired depth in the skin and the ability to protect the delicate microneedles prior to application to the skin.